I regularly run scans with each of them. What I find strange is that Windows Defender and Malwarebytes never find anything. I mean NEVER. Often when I run one of the other programs they'll locate cookies and other potentially unwanted programs but Defender and Malwarebytes never turn up anything, even when I run them first.

Are these programs ineffective or are they merely less sensitive than the others?

Malwarebytes' Anti-Malware has successfully removed 2369 different vendors and 1,800,443,840 total objects worldwide.

MalwareNET™ is our online database which allows you to obtain information about malware that is detected and removed by our product, Malwarebytes' Anti-Malware. Simply click on an item below and a new page will open that shows you the detection rate, the dates the infection was seen and a brief description of the malware.

The real benefit of MBAM is when a system has been infected,the fact that the scans you run pick up nothing says more about your personal policy of computer usage than any shortcomings in the program.

As for Spybot I agree it's not really powerful enough as a frontline utility nowadays but I find it often removes a few leftovers when the other tools have cleaned out the main malware,so it does still have some benefit IMO.

Malwarebytes does not now nor will it ever detect cookies , our users made it VERY clear that they have no desire to see this addition . The same goes for usage tracks , traces like these are handled quite well by multiple tools already .